1. Field of the Invention
The present invention relates to solar cell manufacturing, and more particularly, to a plasma processing apparatus for fabricating thin film solar cells.
2. Background of the Invention
Recently, large-area plasma processing apparatus have been widely used in the semiconductor field, such as thin film deposition or etching, for manufacturing such as flat panels and thin film solar cells. Radio-frequency (RF) power and frequency required for plasma processing are becoming higher and higher with the increase of processing size.
In the current large-area plasma processing apparatus, the technique of double vacuum chambers is widely applied and the plasma reactor is placed inside a vacuum outer chamber, which protects the relatively fragile plasma reactor. However, as the RF power source is independently placed outside the vacuum outer chamber, it is needed to use RF power transmission line to transmit RF signals to an RF electrode inside the plasma reactor. As the vacuum chamber is not completely vacuumed but contains such gases as nitrogen, argon, silane and hydrogen, the condition for discharge can be easily satisfied when high power RF signals pass through the RF power transmission line.
The discharge generated in the vacuum chamber may cause problems as follows: RF signals can not be effectively transmitted to the plasma reactor due to power losses, which may affect the plasma processing. High power discharge may destroy the transmission line, RF power source and other electronic circuits of the apparatus, and even bring about safety accidents. Therefore, how to transmit RF signals effectively and safely has become an urgent problem to be solved for the plasma processing apparatus. Theoretically, increasing vacuum degree can reduce the probability of discharge, but it is hardly possible to create an environment with absolute vacuum. Moreover, the increase of vacuum degree also correspondingly increases the use cost of apparatus.